This invention relates generally to devices and systems for detecting physical conditions and more particularly to a system for detecting abnormal conditions in gas engines. More specifically the invention concerns a system of this character which is capable of detecting abnormal ignition and other abnormalities in a gas-combustion engine and at the same time is capable, upon detecting such an abnormality, of automatically stopping the supply of the fuel gas being injected into the engine.
Most gas engines in the past have been started by ignition systems which ignite fuel gas by means of so-called pilot oil or ignition (spark) plugs. These ignition systems, however, have occasionally been subject to failure of the fuel gas to ignite due to an abnormal condition of the injection valve for the pilot oil or of the ignition plug or, in the case of an injection valve abnormality, to a flow of a great quantity of gas into each cylinder. In the case of such an ignition failure, the gas in still uncombusted state flows into the air intake and exhaust passages and there explodes. In the case where a large quantity of the gas flows into a cylinder, the pressure within the cylinder rises to an extreme value, which is very undesirable.
Accordingly, there arises the need for a system for detecting such ignition failure or abnormal flow of the gas into each cylinder and thereupon automatically stopping the supply of the injected gas. The principal systems of this character known heretofore are the following five.
(a) A system in which an exhaust gas temperature gage is installed in the exhaust pipe to detect any abnormal fall or rise in the exhaust gas temperature.
(b) A system in which the output signal from a device for detecting the pressure within a cylinder is processed as it is by a computer, and quantities such as the maximum pressure within the cylinder and the rate of pressure rise are computed thereby to detect abnormal conditions.
(c) A system in which the exhaust gas within the exhaust pipe is sampled, and defective operation such as ignition failure or sticking of a needle valve is detected.
(d) A system in which the lift of the gas valve is detected by a displacement sensor, and any abnormal operation of the gas valve is detected.
(e) A system in which an orifice is installed within the gas supply passage or pipe, and the difference in the pressures respectively upstream and downstream of this orifice detected thereby to detect abnormalities in the gas flow rate.
The above five systems, however, are accompanied by the following difficulties.
(a) In the system (a), since a relatively long time is required for the detection of abnormalities, the engine operation goes through a number of cycles from the instant of an abnormality occurrence to the stopping of the gas supply, and during this time, unburned gas flows into the intake and exhaust passages.
(b) In the system (b), since the phenomenon occurs at high speed, a computer possessing a large processing capacity becomes necessary for analysis for every cycle, and the constitution of the system becomes complicated.
(c) In the system (c), a relatively long time is required before detection similarly as in the case of system (a).
(d), (e) In the systems (d) and (e), while the phenomenon of abnormal gas flow into the cylinder can be determined, ignition failures cannot be detected.